The present invention relates in general to detonators, and in particular, to electronic detonators that integrate a high voltage switch, an initiator and a fireset.
In various industries, such as mining, construction and other earth moving operations, it is common practice to utilize detonators to initiate explosives loaded into drilled blastholes for the purpose of breaking rock. In this regard, commercial electric and electronic detonators are conventionally implemented as hot wire igniters that include a fuse head as the initiating mechanism to initiate a corresponding explosive. Such hot wire ignitors operate by delivering a low voltage electrical pulse, e.g., typically less than 20 volts (V), to the fuse head, causing the fuse head to heat up. Heat from the fuse head, in turn, initiates a primary explosive, e.g., lead azide, which, in turn, initiates a secondary explosive, such as pentaerythritol tetranitrate (PETN), at an output end of the detonator. In this regard, conventional hot wire igniters cannot directly function a high density secondary explosive and must rely on an extremely sensitive primary explosive to transition the detonation process from the fuse head to a corresponding explosive output pellet. Typically, the firing voltage of hot wire igniters is less than 20 V, the required current is less than 10 amps and the peak power needed to function the detonator is less than 10 watts. As such, it is possible that the voltage and power requirements to function this type of detonator may be encountered from inadvertent sources like static, stray currents and radio frequency (RF) energy.
An electric detonator that serves as an alternative to the hot wire initiator based detonator was developed in the 1940's for military purposes and now has found civilian use for energetics research. This exemplary detonator is known as an exploding bridgewire detonator (EBW), which includes a short length of small diameter wire that functions as a bridge. In use, explosive material beginning at a contact interface with the bridgewire transitions from a low density secondary explosive to a high density secondary explosive at the output end of the detonator. The secondary explosive is normally PETN or cyclotrimethylene trinitramine (RDX). Like conventional hot wire intiators, an EBW cannot directly initiate a high density secondary explosive. To initiate a detonation event, a higher voltage pulse, e.g., typically, a threshold of about 500 V, is applied in an extremely short duration across the bridgewire causing the small diameter wire to explode. The power needed to function this type of detonator is in the kilowatts range. The shockwave created from the bridge wire's fast vaporization initiates the low density pellet, which in turn initiates the high density secondary explosive pellet at the output end of the EBW.
Another exemplary detonator type utilizes an exploding foil initiator (EFI). A conventional EFI includes a thin metal foil having a defined narrow section, and a polymer film layer is provided over the metal foil. A pellet of explosive material is spaced from the polymer film layer by a barrel having an aperture there through. The barrel is positioned over the thin metal foil such that the barrel aperture is aligned with the defined narrow section. To initiate a detonation event, a high voltage, very short pulse of energy is applied across the metal foil to cause the narrow section of the metal foil to vaporize. As the narrow section of the metal foil vaporizes, plasma is formed as the vaporized metal cannot expand beyond the polymer film layer. The pressure created as a result of this vaporization action builds until the polymer film layer is compromised. Particularly, the pressure causes a flyer disk to release e.g., to bubble, shear off or otherwise tear free from the polymer layer. The flyer disk accelerates through the aperture in the barrel and impacts the pellet of explosive material. The impact of the pellet by the flyer imparts a shock wave that initiates the detonation of the pellet and any connected explosive device.